Dear PIC.ers and Javier Puiggros esp.,
..
How to improve the resolution of a PIC 8-bit adc?
If you can afford the processing time (many jobs can), you could
read the port 256 times and summate the adc 8bit result each time
to a 16bit file register pair.
..
Then just throw away the lowest 4 bits, leaving you with a 12bit
result.
..
Of course, this doesn't get around the 8bit quantising of the adc,
but if there is a *little* noise inherent in your measurement, you
can end up with a genuinely higher resolution.
If you have *too much* noise present, this technique can also be
used to `average' a stream of 256  8bit values - just discard the
lower byte result after the routine is finished.
..
Get hold of National Semiconductor's apnote  AN-804
`Improving A/D converter performance using dither.'
..
Best Regards,    John.
email from John Sanderson   /   JS Controls, Boksburg, RSA
Manufacturer & purveyor of laboratory force testing apparatus
and related products and services.
Tel/fax: Johannesburg 893 4154    Cellphone 082 453 4815